Conventional bandgap reference circuits generally develop a constant reference voltage and may use an operational amplifier to cause currents to be equal or to cause certain voltages to be equal. Additionally, conventional bandgap reference circuits may generate a bandgap voltage and then translate the bandgap voltage into a current.
FIG. 1 illustrates one conventional bandgap voltage circuit. An operational amplifier 12 generally forces its inputs to be equal. However, the implementation of the operational amplifier 12 generally limits headroom. The operational amplifier 12 generally requires extra circuitry to maintain stability in the feedback loops. FIG. 1 is generally limited to generating a current that is proportional to absolute temperature (PTAT).
FIG. 2 illustrates a conventional bandgap circuit that can be found in U.S. Pat. No. 4,849,684. The circuit of FIG. 2 is generally limited to generating a current that is proportional to absolute temperature.
FIG. 3 illustrates a conventional bandgap circuit that can be found in U.S. Pat. No. 5,559,425. The circuit of FIG. 3, similar to the circuits of FIGS. 1 and 2, is generally limited to generating a current that is proportional to absolute temperature.
FIG. 4 illustrates a bandgap circuit that can be found in U.S. Pat. No. 4,935,690. The circuit of FIG. 4 is generally limited to presenting either a voltage output, or a current that is proportional to absolute temperature.
FIG. 5 illustrates a bandgap circuit that can be found in U.S. Pat. No. 4,450,367. The circuit of FIG. 5 is generally limited to generating a current that is proportional to absolute temperature.
FIG. 6 illustrates a conventional bandgap circuit that can be found in U.S. Pat. No. 5,451,860. The circuit of FIG. 6 is generally limited to generating a voltage output.